1. Field of the Invention
The present invention relates to a two-piece retainer and a two-piece roller bearing including the retainer. The bearing may be used in a conrod large end of an automotive engine or in an idler of a transmission.
2. Description of the Related Art
In automotive engines, the crank pins and the crank arms are formed integrally with each other, and for this reason, the bearing used in the conrod large end is a two-piece roller bearing. Accordingly, the bearing retainer also has a two-piece construction.
The two-piece retainer is constituted essentially by two halves. The two semi-annular retainer parts are butted to each other at their divided surfaces to form an annular structure. The retainer is guided as the retainer's outer diameter surface makes partial contact with the inner diameter surface of the bearing's outer ring; or if the roller bearing does not have an outer ring but has a retainer, the retainer is guided as the retainer's outer diameter surface makes partial contact with the inner diameter surface of the housing. During this contact, there is a case where a film of lubricant is cut and lost by angled portions, (which include burrs and edges resulting from machining processes; hereinafter this definition applies) that are present on the butting surfaces of the retainer parts. Loss of oil film means insufficient lubrication of the bearing, which can be a cause of reduced life of the bearing.
In an attempt to solve this problem of lost oil film caused by angled portions, there is known a technique as implemented in a roller bearing retainer 1 shown in FIG. 7 according to Prior art 1, where chamfer 5 is provided at the angled portion which is made by a butting surface 3 of the semi-annular retainer part 2 and the part's outer diameter surface 4 (Patent Literature 1). Each retainer part 2 has pockets for holding rollers 6.
However, there is still a risk that new angled portions 7 will be formed along boundary regions between the sloped surfaces of the chamfers 5 and the outer diameter surfaces 4, and loss of oil film will be caused by these angled portions 7.
A potential advantage in this case, however, is that butting two portions each having the chamfer 5 together will form a V-shaped groove, which serves as a lubricant reservoir for improved lubrication by, for example, supplying lubricant to regions where lubrication becomes insufficient due to any reason such as loss of oil film.
Another technique is implemented in Prior art 2 in FIG. 8, where in each region of the outer diameter surface 4 which includes abutting surface 3 a cutoff is made so that a two-piece retainer 1 has a gentler arc surface 9 (Patent Literature 2). In this case, however, there can be cases where the portion including the butting surface 3 is centrifugally expanded in radially outward directions, bringing angled portions 10 into contact with the inner diameter surface of the housing, resulting in loss of oil film. It should be noted here that in this example, there is no lubricant reservoir 8 (see FIG. 7) such as formed in the previous example.
Further, still another technique is implemented in Prior art 3 in FIG. 9, where each region of the outer diameter surface 4 which includes a butting surface 3 is cut off to be a flat surface 11 (Patent Literature 3). In this case again, there can be cases like in the previous example in FIG. 8 where the portion including the butting surface 3 is centrifugally expanded in radially outward directions, bringing angled portions 10 into contact with the inner diameter surface of the housing, resulting in loss of oil film. Note that there is no lubricant reservoir formed in this example, either.